Adaptive control of motor vehicle powertrain

ABSTRACT

A method and system is disclosed for blending between torque maps of a source of propulsion of a vehicle. Embodiments of the present invention are particularly applicable to automatic selection of an alternative torque map in response to a change of vehicle operating condition, for example a change of terrain. Blending according to embodiments of the present invention may substantially avoid a step change in response of the source of propulsion as accelerator position is changed.

FIELD OF THE INVENTION

Embodiments of the present invention relate to adaptive control of apowertrain of a motor vehicle. In particular, embodiments of the presentinvention relate to adaptive control of a source of motive power, forexample an internal combustion engine and in particular, but notexclusively, to the response of the engine to an operator command inconsequence of a change of engine operating mode. The change of engineoperating mode may in turn be related to a change of operating mode of avehicle in which the engine is installed, for example an operating moderelated to the terrain under a vehicle. Aspects of the invention relateto a method, to a system and to a vehicle.

BACKGROUND

Internal combustion engines of vehicles may have operating modes whichmay be selectable by the driver. Thus in some vehicles an economy mode,a normal mode and a sport mode may be provided, each mode having adifferent engine response to one or more commands of the driver.Typically the engine may respond differently in each mode to a giveninput of the accelerator pedal, being least responsive in economy mode,and most responsive in sport mode. In this way driveability of thevehicle can be improved by providing a range of accelerator pedalmovement which is appropriate to, for example, the desired output torquecharacteristic of the engine. Such a system necessarily relies upon anelectronic input from the vehicle driver, for example an acceleratorpotentiometer providing an input signal to an electronic control unithaving a plurality of accelerator pedal position/output torque maps. Themaps may also be referred to as accelerator pedal progression maps orpedal progression maps.

Another kind of operating mode relates to the terrain which a vehicle isintended to cross. U.S. Pat. No. 7,349,776, the content of which ishereby incorporated by reference, describes a vehicle control system inwhich the driver can implement improved control over a broad range ofdriving conditions, and in particular over a number of differentterrains which may be encountered when driving off-road. In response toa driver input command relating to the terrain, the vehicle controlsystem is selected to operate in one of a number of different drivingmodes including one or more terrain response (TR) modes. For each TRmode, the various vehicle subsystems are operated in a mannerappropriate to the corresponding terrain.

In one arrangement, a mode (for example a winter mode) is available inwhich the vehicle is configured to launch from standstill in a forwardgear other than first gear such as a second gear to reduce risk ofexcessive wheel slip. Different modes may have different acceleratorpedal maps (amount of engine torque developed for a given acceleratorpedal position), torque delivery (accelerator pedal maps in combinationwith a rate at which engagement of transmission clutches is controlledto take place thereby determining how aggressively gear shifts takeplace), and transmission shift points as a function of coefficient ofsurface friction. For example, in one or more TR modes the transmissionshift points may be arranged wherein gear shifts take place at lowerspeeds than they might otherwise take place at, and in a more gentlemanner (e.g. at a slower rate).

Thus one or more accelerator/torque maps appropriate to the terrain maybe selectable by the driver. For example when driving in rocky terrain,a high torque output may be indicated for a small accelerator movement,thus giving immediate urge to overcome a rock step. In contrast on sand,a low torque output may be indicated for the same accelerator movement,so as to avoid spinning a vehicle wheel and digging a hole. To someextent the selected torque map may be a matter of judgement related tothe available grip on the terrain.

All torque maps (pedal progression characteristics) associated with anyvehicle operating mode coincide at minimum accelerator position/zerotorque and maximum accelerator position/maximum torque. In between theseconditions, a change of map causes an immediate change of engine outputtorque which may be disconcerting to the vehicle driver, especially ifthe accelerator pedal is not being moved at the time of change.

A change of torque map may also be undesirable at minimum acceleratorposition if the behaviour of the vehicle is not as expected when theaccelerator pedal is next advanced.

If an alternative operating mode is selected by the vehicle driver, achange in the characteristic of engine response is generally not asurprise—the change is in fact expected by the driver and is generallydesirable. However difficulties may arise if the operating mode isautomatically selected in response to a vehicle sensing a change ofoperating condition. Thus, for example a vehicle may detect a change ofterrain from rock to sand and, whilst the accelerator is partly applied,command the vehicle engine to adopt a different torque map. A consequentinstant change in engine response may be disconcerting to the driver,especially if such automatic mode changes are repeated frequently.

Likewise a change of mode as the vehicle is rolling to a halt (minimumaccelerator pedal position) may mean that the next depression of theaccelerator causes the vehicle to accelerate significantly differentlyto expectation.

FIG. 1 shows a known motor vehicle 101 having a powertrain 101P. Thepowertrain 101P includes an engine 121, a transmission 124, a powertake-off unit (PTU) 137, a rear driveshaft or propshaft 131R and a frontdriveshaft or propshaft 131F. The rear driveshaft 131R is operable todrive a pair of rear wheels 113, 114 via a rear differential 135R whilstthe front driveshaft 131F is operable to drive a pair of front wheels111, 112 via a front differential 135F.

The vehicle 101 has an engine controller 121C arranged to receive anaccelerator pedal position signal from an accelerator pedal 161 and abrakes controller 141C operable to receive a brake pedal position signalfrom a brake pedal 163.

In the configuration of FIG. 1 the transmission 124 is releasablyconnectable to the rear driveshaft 131R by means of the power transferunit (PTU) 137, allowing selectable two wheel drive or four wheel driveoperation.

The PTU 137 is also operable in a ‘high ratio’ or a ‘low ratio’configuration, in which a gear ratio between an input shaft and anoutput shaft thereof is selected to be a high or low ratio. The highratio configuration is suitable for general on-road or ‘on-highway’operations whilst the low ratio configuration is more suitable fornegotiating certain off-road terrain conditions and other low speedapplications such as towing.

The vehicle 101 has a central controller 101C, referred to as a vehiclecontrol unit (VCU) 101C. The VCU 101C receives and outputs a pluralityof signals to and from various sensors and subsystems provided on thevehicle 101.

The vehicle 101 has a transmission mode selector dial 124S operable toselect a required operating mode of the transmission 124. The selectordial 124S provides a control signal to a transmission controller 124Cwhich in turn controls the transmission 124 to operate according to theselected mode. Available modes include a park mode, a reverse mode and adrive mode.

The vehicle 101 also has a terrain response mode selector dial 128S. Theterrain response mode selector dial 128S is operable by a driver toselect a required terrain response mode of operation of the vehicle.

It is to be understood that if a user selects the drive mode of thetransmission 124, the engine controller 121C employs a drive modethrottle map to determine the amount of drive torque that the engine 121should produce as a function of accelerator pedal position. If the userselects a ‘dynamic’ TR mode, the engine controller 121C employs a sportmode accelerator (or throttle) pedal progression map instead of thedrive mode accelerator pedal progression map. The throttle maps differin that the sport mode throttle map is arranged to provide a moreaggressive response by the engine 121C to a given initial advance (suchas depression) of the accelerator pedal 161.

Different throttle maps are also employed for different respectiveuser-selectable terrain response modes.

As noted above, in some arrangements the vehicle may be operableautomatically to select an appropriate TR mode for the prevailingdriving conditions.

FIG. 2 shows two different accelerator pedal progression maps in theform of a plot of engine torque output T as a function of acceleratorpedal position P on a scale from 0 to 100% of full scale depression ofthe accelerator pedal 161. Two extreme vehicle operating modes A,B areshown. Mode A is an initially cautious torque map and may correspond forexample to a TR mode suitable for use when driving over sand. Mode B isa more aggressive torque map and may correspond to a TR mode suitablefor use when driving over rock. A driver may select operation accordingto mode A or mode B my means of the TR mode selector dial 128S. At thezero and 100% accelerator positions, the torque maps coincide, but atpart depression of the accelerator pedal significant differences intorque output are apparent.

Thus a switch from mode A to mode B at point C (50% application ofaccelerator pedal) results in an immediate jump to point D, withconsequent increase in engine torque output. The characteristic of lineB is subsequently followed whilst mode B is selected. A correspondingswitch in the reverse direction to mode A results in significant drop inoutput torque. Changes between torque maps generally comprise movementsin the direction of the y axis.

The change in output torque of the engine may take time, and can bedeliberately blended, as illustrated in FIG. 3. Thus the increase frompoint C to point D may be controlled to avoid a step change. For examplea maximum blending rate, say 7 Nm/s may be applied, and/or blending maytake place at a defined rate within a maximum time period, of say 20seconds. A small torque change will blend quickly, and a large torquechange will take longer.

FIG. 4 illustrates a blending at a calibrated rate of, say, 7 Nm/s froma cautious torque map A to an aggressive torque map B. At each timeinterval t=1, t=2 etc., the cautious map approaches the aggressive map,but the shape of the cautious torque map is maintained until blending iscomplete, whereupon the characteristic follows the aggressive map B.Blending is generally in the direction of arrow E. Thus a change inaccelerator position whilst blending is in progress does not change thesensitivity thereof.

Although blending is progressive, nevertheless the vehicle driver willstill be subject to a sudden difference in sensitivity of theaccelerator pedal, as the characteristic switches from the shape of thecautious map to the aggressive map, when blending is complete. Thus ablend may be in progress and have reached point F. Application of theaccelerator pedal will result in an engine torque following the shape ofthe cautious map to point G, and then to follow the aggressive maptowards point H. The step change in pedal response at point G may bedisconcerting to the driver, since further application of theaccelerator pedal suddenly has little effect upon engine torque outputin this example.

What is required is a blending strategy that allows for switchingbetween different torque maps without the vehicle driver being presentedwith a significant and unexpected change in accelerator pedal response.Such a strategy is suitable for a vehicle having manual switchingbetween operating modes, and thus torque maps, and also where switchingis automatic.

It is against this background that the present invention has beenconceived. Aspects and embodiments of the invention may provide amethod, a system or a vehicle in which blending of torque is improved.Other aims and advantages of the invention will become apparent from thefollowing description, claims and drawings.

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided a method ofblending between different characteristics of accelerator pedal positionand output torque in a vehicle implemented by a control system, themethod comprising the steps of: detecting a first operating mode of avehicle and applying a source characteristic; detecting a change ofoperating mode of the vehicle and selecting a target characteristic;blending the source characteristic to the target characteristic at ablending rate, said blending rate being a percentage per unit time ofthe difference between said characteristics, and providing a progressivechange of characteristic throughout the range of accelerator pedalposition.

It is to be understood that reference to ‘percentage per unit time’ of adifference between characteristics, such as 10% per unit time of thedifference, is considered equivalent to ‘proportion per unit time’ ofthe difference, in contrast with an absolute value being a fixedquantity that is independent of the difference, for example a fixedquantity of 7 Nm per unit time.

The characteristic relating accelerator pedal position to output torquemay directly indicate the torque output at the flywheel of an internalcombustion engine, or may represent an analogue thereof, such as one ormore of drive torque at the vehicle wheels, power output, anothermeasure of tractive effort, fuel flow, air flow or any measurableindicator that varies according to accelerator pedal progression andtorque output. The output torque may represent the output of other formsof motive power, such as an electric motor, or an analogue thereof, suchas motor current. A vehicle may have one or more sources of propulsion.For example a hybrid electric vehicle may have an engine and at leastone electric machine operable as a propulsion motor. An electric vehiclemay have at least one electric machine operable as a propulsion motor.

Many suitable analogues are known, so that whilst torque is a convenientdirect measure, embodiments of the invention do not exclude the use ofone or more analogues to define the changing pedal progressioncharacteristic.

Thus for blending to a new torque map, with different torque output fora given position of the accelerator pedal, blending gradually changesthe shape of the characteristic from that of the first mode to that of asecond mode having the target characteristic. The consequence is that astep change in the accelerator pedal position/output torquecharacteristic at a transition point between the two characteristics isavoided.

In one embodiment a maximum rate of change of torque is selectable,optionally by the control system. Thus rate of change may be determinedas a maximum for a vehicle in any operating mode, and is mainly intendedto ensure the comfort and safety of vehicle occupants.

In a refinement the maximum rate of change may be dependent upon acondition of use of the vehicle, such as whether the vehicle is in ahigh or low transmission range, and is intended to avoid unacceptablerates of change of output torque of a source of propulsion which mayaffect for example driveability or refinement of the vehicle in certainoperating modes.

According to embodiments of the invention the time taken for completionof blending may be fixed for all accelerator positions, and be forexample determined by the maximum time taken to achieve the widesttransition at the maximum rate of change. Thus if the widest possibletransition between accelerator pedal progression maps is 140 Nm, and themaximum allowable blend rate is 7 Nm/s, the time taken for completion ofblending may be fixed at 20 s.

In one embodiment, however, transition between source and target torquecharacteristics is at the maximum permissible blending rate for allaccelerator positions, so that where the transition is small, theblending time is correspondingly short.

At a fixed accelerator position according to an embodiment the blendingrate is a percentage of the difference between the source and targetcharacteristics. Blending is considered to be complete when the movingcharacteristic is substantially coincident with the targetcharacteristic, say at greater than 95% completion.

Typically however the vehicle driver will make a change of acceleratorposition during blending from the torque characteristic of one vehiclemode to that of another vehicle mode. According to the present inventionthe degree of completion of the blend is applied to the torquedifference at the new accelerator position in order to allow the blendto continue with reference to the starting characteristic (the sourcecharacteristic) at the new accelerator position. In the alternative theinstant torque characteristic is considered to be the starting point fora new blend to a target torque characteristic, and blending towards thetarget is continued. That is, the degree of completion of the blend isapplied to the torque difference at the new accelerator position and theinstant torque characteristic at the instant degree of completion ofblend. In other words, the blend is not reset and blending started againas if for the first time. Rather, blending continues from the new pedalposition, assuming a proportion of blend is already complete. Thereforeblending to the target characteristic takes place over the remainingproportion of the blend to be completed.

If a further mode change takes place whilst blending is in progress, thepercentage completion of blending may be reset to zero and blendingcommenced from the instant accelerator pedal progression characteristicto the new target accelerator pedal progression characteristic. Otherarrangements are also useful.

A typical refresh rate during blending may be 10 Hz or higher so thatblending is not perceptible to the vehicle driver.

Optionally, said blending rate is a percentage per unit time of thedifference between said characteristics when blending is initiallycommenced.

The method may include the step of maintaining said blending rate thesame for all accelerator pedal positions.

The method may include the step of varying said blending rate dependentupon accelerator pedal position.

The method may include the step of limiting the blending rate such thatit does not exceed a maximum value of absolute rate of change of torque.

Optionally, the maximum value of said rate of change of torque is 10 Nmper second, or less. Other values are also useful.

The method may include the step of determining accelerator pedalposition at a refresh rate of 10 Hz or greater, 20 Hz or greater or anyother suitable value, optionally 100 Hz.

The method may include the steps of: detecting a movement of theaccelerator pedal to a new position; recalculating said blending rateaccording to the difference between said characteristics at the newposition; and blending to said target characteristic from the newposition.

Alternatively the method may include the steps of: detecting a movementof the accelerator pedal to a new position, recalculating said blendingrate according to the difference between the instant characteristic atthe time of said movement and said target characteristic, at said newposition; and blending to said target characteristic from said newposition.

The method may include the steps of: detecting movement of theaccelerator pedal to a new position; recalculating said blending rateaccording to the difference between said characteristics at the said newposition and the percentage of completion of blending when movement ofthe accelerator pedal is detected; and continuing blending to saidtarget characteristic from said new position.

Alternatively the method may include the steps of: detecting movement ofthe accelerator pedal to a new position; recalculating said blendingrate according to the difference between the instant characteristic atthe time of said movement and said target characteristic, at said newposition and the percentage of completion of blending when movement ofthe accelerator pedal is detected; and continuing blending to saidtarget characteristic from said new position.

It is to be understood that, in some embodiments, when movement of theaccelerator pedal is detected, the blending rate may be recalculatedsuch that the proportion of completion of blending when movement of theaccelerator pedal is detected is applied to the target and source torquecharacteristics at the new pedal position. Thus, if when movement of theaccelerator pedal to a new position is detected the proportion ofcompletion of blending represents 40%, the instantaneous torque requiredat the new position of the accelerator pedal is determined to correspondto 40% of completion of a blend between the values of torque at thesource and target characteristics at the new pedal position. Thiscalculation is performed repeatedly whilst the pedal is being moved inorder to give an intermediate accelerator pedal progressioncharacteristic that corresponds to a blend of the source and targetpedal progression characteristics.

The difference between the instant amount of torque applied at the newaccelerator pedal position and the amount that would be appliedaccording to the target characteristic is taken to be the balance of theamount of blending remaining, i.e. 60% in this example.

It is to be understood that in some embodiments, at the new pedalposition blending may be continued at the same percentage per unit timeas was applied prior to detection of movement of the pedal. Thus,blending may continue at the same proportion per unit time of thedifference between the source and target characteristics at the newpedal position. This same proportion per unit time may be applied unlessthe absolute value of blend rate so determined would then exceed amaximum allowable absolute rate, such as a rate of (say) 7 Nm/s. Othermaximum values are also useful. Thus if the blend is 40% complete andthe difference between the amount of torque applied at the currentaccelerator pedal position and the amount that would be applied if thetarget characteristic were applied at the same pedal position is 30 Nm,a blend rate of 10% per second where 30 Nm corresponds to a remainingamount of blending of 60%, would result in an absolute blend rate of 5Nm/s. Since this is less than the maximum allowable value, blendingcontinues at the rate of 5 Nm/s.

We consider next a scenario in which blending is commenced when avehicle mode change takes place between source and target acceleratorpedal progression maps having a torque difference of 50 Nm at theaccelerator pedal position P1 when the mode change is triggered.Blending proceeds at the nominal default blending rate of 10% persecond, i.e. at a rate of 5 Nm/s, which is less than the maximumallowable rate of 7 Nm/s in this example.

When the blend is 40% complete, the accelerator pedal position changesto position P2. The instant torque characteristic as the acceleratorpedal position is changed from P1 to P2 is taken to be the amount oftorque that would be applied at the instant accelerator pedal positionaccording to the source characteristic plus a percentage of thedifference between the source and target characteristics at the instantpedal position, the percentage corresponding to the percentage by whichblending is complete. The blend percentage may in some embodiments becontinually recalculated as the pedal is moved.

When the accelerator pedal reaches the new position P2, blending may inone embodiment continue at the same percentage per unit time of thedifference between the source and target characteristics at the newaccelerator pedal position P2 unless this value would exceed the maximumallowable absolute value (e.g. 7 Nm·s). If the amount would exceed themaximum allowable value, then in some embodiments, a control systemimplementing the method converts the maximum allowable value (in thisexample 7 Nm/s) into a percentage of the difference between the sourceand target characteristics at the new pedal position, and continues at ablend rate of this percentage of the difference between the source andtarget characteristics at the new accelerator pedal position P2.Blending thereby effectively continues at the maximum allowable rate.However, importantly, blending proceeds as a percentage per unit time ofthe difference between source and target characteristics. This has theadvantage that if a change in accelerator pedal position P2 subsequentlytakes place whilst blending is in progress, an instant accelerator pedalprogression characteristic may be generated by the control system asdescribed above having a form as a function of pedal position P that isa blend of the forms of the source and target pedal progressioncharacteristics.

If a blend is progressing at a blend rate below the maximum defaultblend rate of 10% per second due to the absolute value of thisproportion exceeding the maximum allowable absolute value (e.g. 7 Nm/s),when the accelerator pedal is subsequently moved the instantcharacteristic continues to be determined by adding, to the torque valueof the source pedal progression characteristic at the instant positionof the accelerator pedal, a proportion of the difference between thesource and target torques at that position. The proportion correspondsto (and in the present example is substantially equal to) the proportionof the blend that has been completed. This enables the instant pedalprogression characteristic to be defined and followed as describedabove. The control system may continue the blend at the same proportionper unit time of the difference between the source and targetcharacteristics at the new pedal position. Alternatively, the controlsystem may in some embodiments determine whether blending may continueat a higher rate corresponding to the maximum blend rate of 10%, withoutexceeding the maximum absolute value of blend rate, in this example 7Nm/s.

We consider as an example the case where a blend is commenced betweensource and target characteristics having a torque difference exceeding70 Nm at the instant pedal position, for example 140 Nm. At the defaultblend rate of 10% per second, blending would be expected to proceed at arate of 14 Nm/s and take 10 s. However the absolute value of 14 Nm/sexceeds the maximum allowable absolute value of 7 Nm/s. Accordingly, thecontrol system implementing the method determines the proportion of thedifference in source and target torques represented by 7 Nm/s (in thepresent example 5%) and blending proceeds at a rate of 5% per second.The total blend time is therefore expected to be 20 s.

If the accelerator pedal position P subsequently changes when (say) 50%of the blend is complete, the control system may apply the proportion ofcompletion of the blend (50%) to the difference between the instanttorque at the new accelerator pedal position P and the target torque atthe new accelerator pedal position. In an embodiment, the new differenceis considered to represent a remaining amount to be blended of 50% ofthe difference between source and target characteristics. Blendingtherefore continues at a rate of 5% per second of the difference betweenthe source and target characteristics at the new accelerator pedalposition, and would take approximately 10 s to complete. Thus, if theabsolute value of the new difference between source and target torquesat the new accelerator pedal position was 50 Nm, blending would continueat an absolute rate of 2.5 Nm/s for the remaining 25 Nm or torquedifference.

In an alternative embodiment, at the new pedal position, it isdetermined whether blending can continue at the maximum allowable rateof 10% per second of the difference between source and target torquevalues at the new pedal position. In the present example, 10% of thedifference is 5 Nm, resulting in a blend rate of 5 Nm/s. This is lessthan the maximum allowable absolute value of 7 Nm/s and is thereforeallowable. Thus, blending continues at the rate of 10% per second, i.e.5 Nm/s, and it takes only 5 s to blend the remaining 25 Nm of torquedifference.

The method may include the steps of: detecting a movement of theaccelerator pedal to a new position; and blending to the targetcharacteristic from said new position at a maximum blend rate being anabsolute value of rate of change of torque.

This feature has the advantage that a blend may be completed relativelyquickly once a user has moved the throttle pedal.

Optionally the step of detecting movement of the accelerator pedal to anew position comprises detecting an advance of the accelerator pedal toa new position.

The maximum blend rate may be 10 Nm per second, or less, optionallysubstantially 7 Nm per second, optionally a value from around 5 Nm persecond to around 10 Nm per second. Other values are also useful.

Optionally the method includes the further steps of: detecting a furtherchange of operating mode of a vehicle; selecting a new targetcharacteristic; and blending at a blending rate to said new targetcharacteristic from the instant characteristic at the time of saidfurther mode change, and at the instant position of said acceleratorpedal, said re-stated blending rate being a proportion per unit time ofthe difference between the instant characteristic and new targetcharacteristic.

As described herein, the instant characteristic may be calculated as theweighted average of the original source and target characteristics, theweighted average being calculated according to the percentage completionof blending. This feature inherently enables blending of the form of thesource and target characteristics such that a sudden change of form fromthe source to the target characteristics is not experienced by thedriver, in contrast to the known method illustrated in FIG. 4.

In one aspect of the invention for which protection is sought there isprovided an electronic control system for defining the output of asource of propulsion of a vehicle such as an engine in relation to theposition of an accelerator pedal by reference to a plurality of torquemaps held within a memory, said system being adapted to detect a firstoperating mode of the vehicle and apply a source torque map, to detect achange of operating mode of the vehicle and select a target torque map,and to blend the torque map applied to the vehicle from the sourcetorque map to the target torque map at a blending rate defined as apercentage per unit time of the difference between said maps.

The system may be responsive to an automatic change of vehicle operatingmode. The system may be operable to command a change of vehicleoperating mode, optionally in response to one or more sensor inputs.

Optionally the blending rate is selectable. The blending rate may beselectable by the control system. In some embodiments the blending ratemay be user selectable.

Optionally, blending is carried out at a refresh rate of 10 Hz orgreater.

The system may be adapted to detect movement of an accelerator pedal toa new position after blending has commenced, to recalculate the blendingrate according to the difference between an instant torque map and thetarget torque map, and to blend to the target torque map from said newposition.

The instant torque map may correspond to a weighted average of thesource and target torque maps according to a proportion of completion ofblending from the source to the target torque maps.

In an embodiment, the blend rate is determined starting with a knowledgeof the torque difference between the source and target characteristics,a minimum allowable absolute blend time and a maximum allowable blendrate. It is first determined how long the blend would take to completeat the maximum allowable blend rate. If this time period is greater thanor substantially equal to the minimum period, the maximum absolute blendrate is converted to a percentage per unit time of the torque differencebetween the source and target characteristics. Blending then progressesat this proportion per unit time of the difference between thecharacteristics.

If the blend period would be less than the minimum period, then theblend rate is determined as that rate which will result in a blendperiod substantially equal to the minimum period. Thus in oneembodiment, the rate is determined as a percentage per unit timecorresponding to 100/(minimum time penod) per unit time. The blend thenproceeds at this proportion per unit time of the difference between thecharacteristics.

In a further aspect of the invention for which protection is soughtthere is provided a vehicle having an electronic control systemaccording to the preceding aspect. The system may be operableautomatically to change operating mode according to conditions of usewhereby one of a plurality of torque maps is selected for each operatingmode.

Embodiments of the present invention also provide an electronic controlsystem incorporating a method according to an embodiment of theinvention, and a vehicle incorporating the control system and having asystem of changing vehicle mode, typically automatically, according tooperating conditions thereof.

According to another aspect of the invention for which protection issought there is provided an electronic control system for defining theoutput of a source of propulsion of a vehicle such as an engine inrelation to the position of an accelerator pedal by reference to aplurality of torque maps held within a memory, said system being adaptedto detect a source operating mode of the vehicle and apply a source map,to detect a target operating mode and select a target map, and to blendfrom the source map to the target map at a blending rate defined as apercentage per unit time of the difference between said maps.

Aspects of the invention for which protection is sought also provide avehicle having such an electronic control system and a system ofchanging an operating mode thereof.

Within the scope of this application it is expressly intended that thevarious aspects, embodiments, examples and alternatives set out in thepreceding paragraphs, in the claims and/or in the following descriptionand drawings, and in particular the individual features thereof, may betaken independently or in any combination. For example, featuresdescribed in connection with one embodiment are applicable to allembodiments unless such features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic illustration of a known motor vehicle;

FIGS. 2 to 4 represent prior art blending of torque maps;

FIG. 5 is a schematic illustration of a motor vehicle according to anembodiment of the present invention; and

FIG. 6 illustrates torque blending according to an embodiment of theinvention.

DETAILED DESCRIPTION

FIG. 5 is a schematic illustration of a motor vehicle 201 according toan embodiment of the present invention. Like features of the vehicle 201of FIG. 5 to those of the vehicle 101 of FIG. 1 are shown with likereference numerals prefixed numeral 2 instead of numeral 1. Thus engine121 of the vehicle 101 of FIG. 1 corresponds to engine 221 of thevehicle 221 of FIG. 5.

The vehicle 201 has a VCU 201 programmed with accelerator pedalprogression maps that are used to determine engine torque T as afunction of accelerator pedal position P.

FIG. 6 shows a plot of engine torque (T) against percentage of maximumaccelerator position (P). A cautious characteristic is marked A, and anaggressive characteristic is marked B.

In the event of a change of vehicle operating mode whereby for examplethe cautious characteristic is blended to the aggressive characteristic,blending is in the direction of arrow E, and the progress of the blendis indicated at time t=1, t=2 etc.

According to the embodiment of FIG. 5 and as illustrated in FIG. 6, theengine torque characteristic progressively changes shape as the blendprogresses so that, for example, an increase of accelerator pedalposition at point F will follow the blending characteristic towardmaximum (point H). Such a blend has no significant step change, incontrast to FIG. 3 where a change in accelerator pedal position from P1to P=100% along line FGH results in a step change in the response atpoint G.

In one embodiment the blend output, at any stage during the blend, is aweighted average of the torque of the original mode and the torque ofthe newly demanded mode. A change in accelerator position duringblending causes the vehicle engine to follow the instant torquecharacteristic at the percentage of completion of the blend, asdescribed in more detail above and below.

The instant torque characteristic is determined as the weighted averageof the torque of the original mode and the torque of the newly demandedmode at the instant position of the accelerator pedal. The weightedaverage is given by the percentage completion of the blend. Thus if ablend is 40% complete and the accelerator pedal position is changed, theVCU 201C calculates the amount of torque to be generated by the engine221 at a given instant as the amount of torque that would be developedat the instant accelerator pedal position according to the original mode(e.g. by reference to progression map A) plus 40% of the differencebetween the amount of torque that would be developed at the instantaccelerator pedal position according to the original mode and that whichwould be developed at the instant accelerator pedal position accordingto the newly demanded mode. This feature has the advantage that theinstant pedal progression map gradually changes form from that of theoriginal mode to that of the newly demanded mode as blending progresses,rather than retaining the form of the original mode, as per the knownarrangement of FIG. 4.

In other words, in the embodiment of FIG. 5, in the event that a changein accelerator pedal position takes place, the value of engine torquecorresponds substantially continuously to a weighted average of thetorque of the original mode and the torque of the newly demanded mode ata given pedal position, the weighting being given by the percentage ofcompletion of blending. The weighting may change as blending progresseseven whilst the accelerator pedal 261 is being moved.

The rate of blending may be a fixed percentage per unit time, forexample 10% per second. The absolute value of the rate of blending mayhowever be capped at a prescribed maximum allowable rate of blending.The prescribed maximum rate may be any suitable rate, for example 7Nm/s, 10 Nm/s or any other suitable value. It is to be understood thatsuitable values may be determined empirically.

The fixed rate of blending may be continually converted by the VCU 201Cinto a percentage per second value based on the current torquedifference between the original and target characteristics.

It is to be understood that the feature of a progressive change ofcharacteristic from the original to the target characteristic throughoutthe range of accelerator pedal position is fundamental to embodiments ofthe present invention.

In one example, at a given position of the accelerator pedal 261, atorque difference of 140 Nm may exist between characteristics. At ablending rate of 10% of this value, the blending rate would be 14 Nm/s,which exceeds the maximum allowable blending rate of 7 Nm/s for thepresent embodiment. At a blending rate of 7 Nm/s, the time of blend is20 seconds, and accordingly a blending rate of 5% per second is appliedto give a continuous transformation of the torque characteristic betweenold and new. The blending rate of 5% per second may be maintained evenif the driver subsequently changes the accelerator pedal position.However if under these circumstances the blending rate would exceed 7Nm/s, the maximum allowable blending rate would be employed, which inthe present embodiment is 7 Nm/s. In some embodiments the percentageblending rate represented by the maximum allowable blending rate wouldbe recalculated and applied.

In an alternatively method, the blending rate may be recalculateddepending on the difference between torque values of the original(source) and newly demanded (target) modes at the new accelerator pedalposition. In some embodiments the blending rate may be recalculateddepending on the difference between torque values of the instant torquecharacteristic (being a weighted average of the original and targetcharacteristics) and target characteristic at the new accelerator pedalposition.

It will be appreciated that embodiments of the present invention avoid astep change in the sensitivity of the position of the accelerator pedal161, so that a small change of pedal position during blending will allowthe vehicle driver to become accustomed to the changing shape of torquecharacteristic.

It is to be understood that where the target blending rate is a fixedamount per unit time, say 10% per second, the target blending rate maybe substantially equal to 10% per second up to the maximum allowableabsolute value of (say) 7 Nm/s.

Thus, where a torque difference of (say) 70 Nm applies, the time ofblend may be 10 seconds at a blending rate of 7 Nm/s (10% per second),corresponding to the maximum allowable rate. If the torque difference isless than 70 Nm, then the blending rate may be set at 10% of thedifference. In the case of a difference of 50 Nm, the blending rate willbe 5 Nm/s.

With reference to FIG. 6, a percentage progression of blending at 50%accelerator position has a greater absolute effect on engine torque thanthe same percentage change at 90% accelerator position. Thus the changerepresented by double headed arrow 11 is greater than that of arrow 12,and in consequence the torque characteristic changes progressivelybetween characteristic A and characteristic B.

It is to be understood that as described above, the time taken forprogression to a target torque map may be set in dependence upon themaximum rate of blending which is acceptable to a vehicle driver withoutcausing a disconcerting effect. As described above this rate may bequite low, e.g. 7 Nm/s, in relation to a maximum difference in torquemaps of say 140 Nm. At a steady state such a blend will take 20 seconds.As the torque maps converge, however, the absolute difference issmaller, and accordingly transition time at the maximum rate is alsosmaller. This can be disconcerting to a driver. However embodiments ofthe present invention are distinguished in that that for each positionof the accelerator pedal, the transition between torque maps (i.e. theblend) is made in percentage steps rather than in absolute amounts.Thus, as the absolute difference between torque maps reduces, theabsolute blend rate (in Nm/s) reduces accordingly.

During blending the refresh rate of determining accelerator pedalposition may be any suitable value such as 50 Hz or higher. This meansthat the existing (source) and target torque characteristics arecontinually assessed at the refresh rate to determine the instant torqueto be demanded from the engine, and at a rate which the vehicle driverwill not notice.

As described above, a change in accelerator position during blendingcauses the vehicle engine 221 to follow the instant torquecharacteristic at the percentage of completion of the blend. Thus forexample an increasing (advancing) accelerator pedal 161 may shift apartly completed blend from point J to point K of FIG. 6. This change iscomputed virtually instantaneously at a refresh rate of 50 Hz, and thedriver experiences an increased torque output from the engine 221 inresponse to advancing the accelerator pedal 161.

In one embodiment, the new torque output (K) is considered the startingpoint for a new blend toward a target torque (L) on the targetcharacteristic at an unchanged throttle opening, and a new blend iscommenced, preferably at the maximum permissible rate.

Further changes in throttle have the same effect.

Alternative strategies may retain the percentage completion of blendingat point J (corresponding to accelerator pedal position P1), and applyit to the target and existing torque characteristics at point K (L & M).Thus if point J represents 40% completion of blend, point K isdetermined as 40% of completion of a blend between points M & L, and theblend is continued from point K to point L. It is to be understood thatthe position of point K is of course defined with respect to thepercentage of completion of blending, in order that the instant torquecharacteristic itself represents a blend between the source and targetcharacteristics. This allows a driver to gain familiarity with thechanging torque characteristic from characteristic A to B as the blendtakes place.

The blend may continue at point K towards point L at the same percentageper unit time of the difference between the target and sourcecharacteristics (the difference between characteristics A and B at pedalposition P2) as was employed at accelerator pedal position P1. Thus ifthe percentage blend rate was 10% per second of the torque differencebetween points E and F, the blend may continue from point K to point Lat 10% per second of the torque difference between points M and L. Ifthis value would exceed the prescribed maximum allowable rate of change(in the present embodiment this is 7 Nm/s) then the blend may be capped,and continue at a proportion per unit time corresponding to the maximumallowable absolute rate, such as 7 Nm/s. Other arrangements are alsouseful.

At a refresh rate of 50 Hz, the recalculation of blending is alwaysfaster than movement of the accelerator pedal position, and thusimperceptible to the vehicle driver.

It is to be understood that embodiments of the invention are suitablefor use with vehicles in which the transmission 124 is arranged to driveonly a pair of front wheels 111, 112 or only a pair of rear wheels 114,115 (i.e. front wheel drive vehicles or rear wheel drive vehicles) orselectable two wheel drive/four wheel drive vehicles. Embodiments of thepresent invention may be suitable for vehicles having more than fourwheels or less than four wheels.

A method and system is disclosed herein for blending between torque mapsof a source of propulsion of a vehicle. Embodiments of the presentinvention are particularly applicable to automatic selection of analternative torque map in response to a change of vehicle operatingcondition, for example a change of terrain. Blending according toembodiments of the present invention may substantially avoid a stepchange in response of the source of propulsion as accelerator positionis changed.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, means “including but not limited to”, andis not intended to (and does not) exclude other moieties, additives,components, integers or steps.

Throughout the description and claims of this specification, thesingular encompasses the plural unless the context otherwise requires.In particular, where the indefinite article is used, the specificationis to be understood as contemplating plurality as well as singularity,unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith.

The invention claimed is:
 1. A method of blending between differentcharacteristics of accelerator pedal position and output torque in avehicle, the method being implemented by an electronic control systemand comprising: detecting a first operating mode of a vehicle andapplying a source torque map corresponding to said first operating mode;detecting a change of operating mode of the vehicle from said firstoperating mode to a second operating mode and selecting a target torquemap corresponding to said second operating mode; blending by theelectronic control system the characteristic applied to the vehicle fromthe source torque map to the target torque map at a blending rate, saidblending rate being a percentage per unit time of the difference betweensaid source and target torque maps; and controlling a powertrain of thevehicle to output a torque in accordance with the blending between thesource and target torque maps.
 2. The method according to claim 1whereby said blending rate is a percentage per unit time of thedifference between said source and target torque maps when blending isinitially commenced.
 3. The method according to claim 1, and includingone or more of the steps of: maintaining said blending rate the same forall accelerator pedal positions; varying said blending rate dependentupon accelerator pedal positions; limiting the blending rate such thatit does not exceed a maximum value of absolute rate of change of torque;and determining accelerator pedal position at a refresh rate of 20 Hz orgreater.
 4. The method according to claim 1, including the step oflimiting the blending rate such that it does not exceed a rate of changeof torque of 10 Nm per second.
 5. The method according to claim 1, andincluding the steps of: detecting a movement of the accelerator pedal toa new position; recalculating said blending rate according to thedifference between said source and target torque maps at the newposition; and blending to said target torque map from the new position.6. The method according to claim 1, and including the steps of:detecting a movement of the accelerator pedal to a new position,recalculating said blending rate according to the difference between theinstant torque map at the time of said movement and said target torquemap, at said new position; and blending to said target torque map fromsaid new position.
 7. The method according to claim 1, and including thesteps of: detecting movement of the accelerator pedal to a new position;recalculating said blending rate according to the difference betweensaid source and target torque maps at the said new position and thepercentage of completion of blending when movement of the acceleratorpedal is detected; and continuing blending to said target torque mapfrom said new position at said recalculated blending rate.
 8. The methodaccording to claim 1, and including the steps of: detecting a movementof the accelerator pedal to a new position; and blending to the targettorque map from said new position at a maximum blend rate being anabsolute value of a fixed rate of change of torque.
 9. The methodaccording to claim 8, wherein the step of detecting movement of theaccelerator pedal to a new position comprises detecting an advance ofthe accelerator pedal to a new position.
 10. The method according toclaim 8 whereby the maximum blend rate is 10 Nm per second, or less. 11.A method according to claim 1, and including the steps of: detecting afurther change of operating mode of a vehicle; selecting a new targettorque map; and blending at a blending rate to said new target torquemap from the instant torque map at the time of said further mode change,and at the instant position of said accelerator pedal, said re-statedblending rate being a percentage per unit time of the difference betweenthe instant torque map and new target torque map.
 12. The methodaccording to claim 1 wherein said first operating mode comprises a firstterrain type and wherein said change of operating mode comprises achange to a second terrain type.
 13. The method according to claim 1wherein said first operating mode comprises one of an economy mode ofoperation, a normal mode of operation, and a sports mode of operationand wherein said change of operating mode comprises a change to anotherof said economy, normal and sports modes of operation.
 14. The methodaccording to claim 1 further comprising the step of operating thevehicle using the target torque map.
 15. A vehicle electronic controlsystem for defining output torque in relation to the position of anaccelerator pedal by reference to a plurality of torque maps held withina memory, said system comprising at least one controller that isconfigured to: detect a first operating mode of the vehicle and apply asource torque map corresponding to said first operating mode, detect achange of operating mode of the vehicle from said first operating modeto a second operating mode and select a target torque map correspondingto said second operating mode, blend the torque map applied to thevehicle from the source torque map to the target torque map at ablending rate defined as a percentage per unit time of the differencebetween said maps, and control a powertrain of the vehicle to output atorque in accordance with the blending between the source and targettorque maps.
 16. The system according to claim 15, and responsive toautomatic change of vehicle operating mode.
 17. The system according toclaim 15, wherein said blending rate is selectable.
 18. The systemaccording to claim 15, and adapted to detect movement of an acceleratorpedal to a new position after blending has commenced, to recalculate theblending rate according to the difference between an instant torque mapand the target torque map, and to blend to the target torque map fromsaid new position.
 19. The system according to claim 18 wherein theinstant torque map corresponds to a weighted average of the source andtarget torque maps according to a percentage of completion of blendingfrom the source to the target torque maps.
 20. A vehicle having anelectronic control system according to claim 15, and a system ofautomatically changing operating mode of the vehicle according toconditions of use whereby one of a plurality of torque maps is selectedfor each operating mode.